There have been proposed a number of foundry binder compositions which are cured by reacting with a polyisocyanate. Some examples of these are disclosed in U.S. Pat. No. 3,925,296 which discloses binders comprising, in combination with an organic polyisocyanate, either a phenolic compound having at least two phenolic-OH groups, or a condensation product of a furan alcohol and an aldehyde, or a mixture of both of these. We have found that cores formed by use of binders disclosed in this U.S. Patent suffer from the disadvantage that the strength of the cores deteriorates unduly if the cured cores are stored.
Further examples of foundry binder compositions which are used in conjunction with polyisocyanates are disclosed in U.S. Pat. No. 3,429,848. This patent discloses the use, as a foundry binder, of condensation products obtained by reacting phenols with aldehydes. One disadvantage of the use of these condensation products as foundry binders is that water is produced in the condensation reaction. If water is present in the binder when this is mixed with the polyisocyanate, the water tends to react with the polyisocyanate so that the amount of polyisocyanate necessary to achieve a core having a required strength is greater than the amount which would be necessary if the foundry binder was anhydrous.